To promote correct understanding about radiation, radiation counters are now widely used for educational purposes. A radiation counter which detects α-rays and β-rays respectively, has been developed and is available commercially, but there is no portable counter for educational use which detects α-rays. People in general are very concerned about plutonium because of its toxicity and possible use in nuclear weapons. In this regard, we have developed a portable α-ray counter in order to demonstrate the nature of a-emitting radionuclides such as Pu-239. We use a Si surface barrier type semiconductor as a detector, and the total system is compact and light in weight, easily handled and inexpensive. Four kinds of samples which exist around us are prepared.
Two kinds of major techniques are usually applied to measurement of the ionizing component of the cosmic ray dose rate. One is a “precise method” by which the cosmic ray dose rate is obtained from the difference between the reading of an ionization chamber and that of a gamma ray detector such as a NaI(T1) scintillation detector. The former detects both gamma ray and cosmic ray, and the latter only gamma rays. The other is the “simplified method” by which the cosmic ray dose rate is obtained from the count rate above 3MeV of the gamma ray detector based on the assumption that the cosmic ray dose rate is proportional to the count rate. It is reasonable to apply the simplified method in the open air near the ground since the cosmic ray spectrum does not change much. However, attenuation of low energy component by building materials must be considered when the simplified method is applied to indoor measurement because the cosmic ray spectrum may be changed. From a series of measurements by the precise method with a spherical air equivalent ionization chamber of 14 liters and a 3″ diameter spherical NaI(T1) scintillation detector under several environmental coditions, proportionality was found between the cosmic ray dose rate and the count rate above 3MeV. The proportional constant was evaluated to be 20±1.4nGy/h/cps. Also, no apparent difference in the proportional constants was found between indoor and outdoor. It is concluded that the simplified method can be applied to indoor measurement as well as outdoor measurement of the cosmic ray dose rate.
Advanced analytical techniques have enabled us to measure low elemental concentrations in environmental samples. Soil-to-plant transfer factors (TfS) of selected radionuclides have been collected using the stable elements. The TfS for stable elements, however, tend to be smaller than those of the radioisotopes. This might be mainly due to the difference in the ratio of extractable phase. In this study, the extractabilities of three elements (Mn, Zn, Sr) from an agricultural soil were examined with HCl solutions and compared between the stable elements and the radioisotopes (54Mn, 65Zn, 85Sr). Though all extraction ratios increased with HCl concentration, the ratios showed large differences between the stable elements and the radioisotopes. Almost all the 54Mn and 85Sr and about 60% of 65Zn were extracted by 2 N HCl, whereas the extraction ratios of the stable elements were lower by a factor of 2 to 13. These results suggest that stable elements are present in an unexchangeable form to a greater extent than the radioisotopes. Then transfer factors of stable elements would lead to underestimating the intake of anthropogenic radionuclides through the soil-plant pathway.